Insulated electric cable



Sept. 6,1938. E. w. TROLANDER ET AL 2,129,157

INSULATED ELECTRIC CABLE Filed April 10, 1936 F/LM cam/v6 A/vc/m/w/vs"ZO/VE F/LM #vsumw/va COMP05/7/0/V 03W .9 diarnc y.

?atented Eept. 1%38 uru'rso STATES Z,i2s,157

.FFWE

son, Chicago, 111., assigncrs to Pyroxylin Prodnets, 1110., Chicago,Ill, a corporation of Illlnois Application April 1W,

12 Claims.

This invention relates to improved insulated electrical conductors andmore specifically to high tension conductors such as those used in theignition system of internal combustion engines.

One object of the invention is to provide an improved coating over aflexible insulation such as rubber and rubber substitutes, which coatingis impervious .to water, oils, ozone, acids, etc. thus protecting theinsulating composition from deterioration and injury by such injurioussub stances.

Another object is to provide an insulating structure that will retainits flexibility and remain intact over a wide range of temperature, sothat it will withstand high temperatures without deterioration withresulting embrittiement, and will also not become stiff and brittle atlow temperatures. A particular object is to provide an insulating sleevethat does not deteriorate so as to lose its insulating properties, orbecome weakened and break down in the presence of oils even when'exposedto such oils at relatively high temperatures.

A still further and specific object is to provide an insulated conductorhaving a flexible cellulose ether base outer coating, said coating beingsoft and pliable andat the same time free from stickiness or tackinessso that the coating does not adhere to itself when the insulated cableis wound on a spool or roll, and which will lurthcr= more have a surfacewhich will be suiilciently slippery and tough to enable the conductorsto be easily pulled through a conduit and permit the surfaces to beeasily slipped over one another.

Other objects of the present invention center about the provision of acoating material having a cellulose ether base and modifying agents torender the same'capable of meeting the above conditions. Other andancillary objects will be found in and be apparent from the followingspecifications and claims.

In our copending application Serial No. 534,612, filed May 2, 1931, novaPatent No. 2,061,528, issued November 17, 1936, we have described anelectrical insulation that can be produced at a relatively low cost,which insulation is suitable for many purposes. However, the presenttype and design of automotive internal combustion engines, andespecially those used on some of the newer models of trucks and buses.expose the ignition cable to extremely severe coriditions. The conductorshould withstand temperatures as high as'240 F. to 300 F., or higher,for relatively long periods of time with no serious impairment of itsprotective properties. Also the 1936,, Serial No. @3393 (Q1. Nil-264)conductors may be covered with hot lubricatin oils, or it may benecessary to remove spark plugs and flex the cables at low temperatures.With high compression engines, higher voltages are used, which increasethe rate of ozone generation. Under such severe conditions theconductors heretofore available will break down in a few weeks, and mustbe replaced. Automotive conductor cable calls for a high degree ofelastlcity in a cable coating, in addition to flexibility, 1 andordinary bases and fiexibilizing plasticizers are not suitable forcable.

Our invention provides a conductor capable of meeting these severeconditions, and provides a conductor having at least two or three'timesthe efllcient life oi conductors heretofore available.

it has long been lsnown to insulate a conductor with rubber insulation.The rubber insulation, however, rapidly breaks down under the severeexposure such as to hot oil, the ozone generated by the high tensioncmrent, etc. One method of protecting the rubber is described in ouraforementioned applicationseriall los534,612. Another method is to weavea braid over the rubbar, and coat the braid with a nitrocellulose baselacquer. Still another method is to wrap varnished carnbric over therubber base insulation, place a braid over the varnished cambric, andfinally a coating oi nitrocellulose base lacquer over the braid. In allor" these methods, the nitrocelluose coating may be exposed totemperatures above its decomposition point, so that the coatingdeteriorates rapidly, becoming still and brittle and finally crackingand exposing the rubber underneath. Cellulose ester coatings are notsatisfactorily resistant to the more severe exposures in the automotivefield.

Furthermore, cable which has covering, such as a cotton braid or a paperstrip or cord winding, protected by cellulose esters, is subject toembrittlement and destruction of the cellulose itself, in spite of itsprotection. By use of the present invention, such cellulose material canbe exposed without destruction, to temperatures which will destroycellulose alone. or cellulose protected by cellulose esters. I

In the accompanying drawing there are shown several forms of cableembodying the present invention, the character of the coating being more50 particularly set forth in the detailed explanation.

Fig. 1 shows a rubber insulated conductor cable coated with a film ofcellulose ether base, anchored to the rubber bye. suitable priming coat.

Fig. 2 represents an electric conductor heavily 55 insulated by afiexible elastic composition protected with a cotton braid, which iscoated with the essential protecting film.

In the drawing l0 illustrates a single wire conductor housed as usual ina rubber insulation sleeve II. The zone designated i! represents abonding composition between the ultimate outside filmy sleeve or coatl3. and the rubber II, it being understood that the layer I 2 is not adistinct and separable layer, but an anchoring or merging layer betweenthe composition of the coat I! and the rubber composition l I. Fig. 1shows the cable wrapped about a mandrel ll, thus producing stretch inthe rubber and its coating, at the part" designated l5. It is highelasticity at this point that is a rigid requirement, and the stretchedfilm must remain stable and resistant to oil,"

, ozone, and heat, and the film must not break to expose the rubberbeneath it to oil, air or ozone.

In Fig. 2 the conductor is shown as a flexible group 20 of fine wires,covered as usual with a sleeve of rubber composition 2|, and thenprotected with a braided sleeve 22 as of cotton threads. The sleeve isthen covered and/or impregnated with film 23 of the present invention.Likewise a mandrel 24 is shown over which the cable may be bent,producing stretch at 25. The

stretched film may adhere to and must protect the braid, withoutbreaking, so as not to allow oil, air or ozone, acids and the like toenter and affect the braid or the rubber.

We have discovered that these difiiculties may be avoided, and theinsulation protected against the most severe conditions encountered inconnection with internal combustion engines by the use of a celluloseether base protective coating or film. A cellulose ether such as ethylcellulose when used alone, however, is not satisfactory, and modifyingagents must be used therewith as described herein below.

the cellulose ethers. Cellulose ethers so plasticised give protectivecoatings or films having new and unusual properties. For example we havefound that ethyl cellulose and the glycerol ester of sebacic acid may beused to produce films, which are substantially oil-proof, which areunaffected by ozone, which are highly flexible and elastic attemperatures of 0 I". or below, which will remain flexible afterexposure for along period of time at temperatures as high as 325' l, andwhich are relatively stable even at temperatures of 400 I". or higher.

The use of these polyhydric alcohol esters of the higher dibasicaliphatic acids alone with the cellulose ethers is, however, apt toproduce films which will not readily slip over each other. This isobjectionable in many instances, as for example, in pulling a conductorcable througha conduit in which there are other conductors, since thecables are apt to be damaged unless they have sufiicient "slip" over oneanother. Furthermore, the friction may be excessively high, resulting inexcessive mechanical wear where thesurfamlrof two cables rub over eachother during movements caused by vibration or otherwise. I We havediscovered that this can be avoided by the addition of lubricatingagents. While a conductor having a film with no lubricating agent may besurface lubricated, i. e. a lubricant simply wiped over the surface, weprefer to incorporate a suitable lubricant in the film itself, sincesurface lubricants tend to disappear in a short time. We have discoveredthat certain of the non-drying animal and. vegetable oils may beincorporated directly into the films without loss of the above-mentioneddesirable properties. Mineral oils may also be used, but are not assatisfactory as the animal and vegetable oils.

The protective coating or film of our invention includes a celluloseether and a polyhydric alcohol omega-omega dibasic higher aliphatic acidester as the essential plasticizer, and with or without a lubricatingagent incorporated therein. It is to be understood that we maysubstitute other plasticizers for the softening or flexibilizingfunctions of the essential plasticizer, retaining sufllcient polyhydricalcohol-dibasic acid ester for the elasticizing property.

Our protective film or coating may be conveniently applied by dissolvingthe aliphatic cellulose ether and plasticizing ester, and preferably thelubricating agent in a suitable solvent,

applying the solution tothe surface to be pro- I tected, and allowingthe solvent to evaporate, whereby the fllm or coating is deposited onthe said surface. While such protective films or coatings may be applieddirectly to the rubber insulation, we prefer to interpose a fabric suchas a cotton braid between the rubber insulation and the protectivecoating, as shown in Fig. 2. When the film has a high percentage of theessential plasticizer itadheres well to the rubber, but in cases whereadherence is poor, the rubber may be coated twice. The first layer ll,may be a thin layer of the plasticizing ester, or a layer of celluloseether which is rich in the plasticizing agent to the point of beingsomewhat tacky when dry. Upon this anchoring layer, the final layer maybe'applied. Intermediate layers are not excluded, but for practicalpurposes, are not necessary.

The following discussion relates to the final coats l3 and 23. The ratioof cellulose ether to total plasticizer may be varied within wide limitsdepending upon the degree of flexibility desired. However, the amount ofelasticizlng plasticizing ester must be sufilcient, although variable,to secure the desired degree of elasticity. stability and resistance tobreaking, oil, and ozone at the points II and 25, according tocommercial specifications. The following examples are given by way ofillustration, but it is to be understood that wide variations may bemade both in the materials used and in the proportions thereof withoutdeparting from the spirit of the invention.

In the above example the neats-foot oil acts as a lubricant. Such acomposition gives a protective coating that is flexible, highlyresistant to lubricating oils, substantially unaffected by clone,

and which is stable at any temperatures likely to be encountered whenused in connection with internal combustion engines.

Example II Parts by weight Non-volatile:

In the above composition a part of the polyhydric alcohol dlcarboxylicaliphatic acid ester has been replaced with another plasticizer, namelybutyl acetyl ricinoleate for the softening or flexibilizing function.The neats-foot oil is used as the lubricating agent, and it is to beunderstood that such agents may aid in softening or fiexibilizing tosome degree.

In some cases, as for example-on airplane engines, an entirelyflame-proof coating ishighly desirable. We are able to make such acoating using our composition with an added fire-proofing agent, asillustrated by the following example:

Emmple III Parts by weight Non-volatile:

Ethyl cellulose 55 Glycerol ester of sebacic acid 34 Chlorinateddiphenyl (liquid product)" 3d Cocoanut oil 12 Volatile:

Anhydrous ethyl alcohol Toluol 220 The chlorinated diphenyl is afire-proofing agent primarily, but to some extent may act as a plas-'ticizer. The cocoanut oil is a lubricating agent. Coatings made from theabove composition will not support combustion, and are of great valuefor use in ignition cables where non-inflammability is desired.

Toluene Example V Parts by weight Non-volatile:

Methyl cellulose 4 Ethyl cellulose 35 Glycerol ester of sehacic acid 2'7Butyl acetyl ricinoleate 5 Neats-foot oil 7 Volatile:

Water 16 Anhydrous ethyl alcohol 35 Butyl alcohol. 10 Toluol In theabove formula the methyl cellulose is first dispersed to a. colloidalform as a sol or gel in water, and this dispersion used" in compoundingwith the other ingredients. This does not make an excellent film for thepurpose of the invention, and the exampleonly illustrates the factsmentioned concerning methyl cellulose and mixtures of ethers.

For the sake of clearness and simplicity in the above compositions ethylcellulose has been predominantly used as an example of the aliphaticether of cellulose. It is presently preferred, be-

cause of its availability and'becsuse it is highly satisfactory for thepurposes of the invention. We have found that other aliphatic celluloseethers (excepting methyl cellulose) such as propyl cellulose, butylcellulose, etc. may be used in place of the ethyl cellulose in thepractice of our invention. Methyl cellulose.of the character nowcommercialy available is not useful as the sole cellulose ether base,but it is permissible as a diluent for the ultimate purposes of theinvention. Methyl cellulose requires a different type of solvent thanits higher homologs beginning with ethyl cellulose, and the aromaticcelluiose ethers. Because it is too much affected by water, andfurthermore requires solvents including water, it should not be used asthe entire cellulose ether for this invention. Several cellulose ethersmay be used together as the cellulose ether of this invention, and smallamounts of; methyl cellulose ether may be tolerated in such mixtures.

The preferred cellulose ethers are the aliphatic ethers having two ormore carbon atoms in the aliphatic radicle. While the aromatic celluloseothers are useful in our protective coating, we have found they have atendency to soften at higher temperatures. Cable covered with a filmhaving aromatic cellulose ethers, and no aliphatic cellulose others aresuitable for use where they are not exposed to melting or softeningtemperatures. We may, in general however, substitute an aromaticcellulose ether, as for example benzyl ccllulose, for a part of thepreferred aliphatic cellulose ether. Thus we may use, for example, equalparts of benzyl cellulose and ethyl cellulose, or one part benzylcellulose with three parts ethyl cellulose. Ingeneral, however, we havefound that the best results are secured where ethyl cellulose is used asthe major constituent of the cellulose ether content.

Likewise for the sake of clearness and simplicity in the abovecompositions we have shown the .glycerol ester of sebacic acid as theessential plasmore of the dicarboxylic acids may be used in ourinvention. The various esters may be mixed as well as being used alone.

It is also to be understood that other modifying agents such as coloringmaterials as for example dyes, pigments, finely divide metals such asthe so-called aluminum or gsud bronzes may be added to give the desiredcolor efiect. Example 11 shows carbon black as a coloring agent. ExampleIII shows a fire-proofing agent. We may also add waxes to decrease themoisture vapor permeability, or for other purposes, also resins, as iswell understood in the art.

Electrical conductors made according to our process have the surprisingproperty of protectproducts of 'thenitrocellulose lacquers heretoforeused cause the braid to be rapidly weakened. Our protective coating notonly does not decompose to liberate products which weaken the braid, butactual tests indicate that the braid is protected and its life prolongedby our coating. In certain types of busesand trucks the life of theignition cable heretofore available has been very short. Cables madeaccording to our process have a useful life many times longer than theignition cables heretofore available.

Where the term rubber" is used in the specification and in the claims,it is intended to include ordinary rubber as it has long been known incomposition form for insulation purposes, and also other substances orcompositions used as substitutes for such rubber as insulation onelectric conductors, alone or in mixtures. There are various suchsubstitutes now known and used, such as "Duprene" made by'the Du PontCompany of Wilmington, Delaware, U. B. A.; Plioform made by the GoodyearTire and Rubber Company of Akron, Ohio, U. S. A.; "Thiokol made by theThiokol Corporation, Yardville, New Jersey. U. S. A.; "KoroseaY made bythe Goodrich Rubber Company, Akron, Ohio, U. S. A.; balata, and othernatural or synthetic rubbery products.

The fact that rubber in electric conductor cable is subject to injuryfrom numerous sources makes it necessary to protect the same by housingit in some envelope such as the sleeve described. The film-type ofsleeve covered by this invention provides the desired protection byreason of the essential combination of cellulose ether .as a basematerial and a modifying ester of polyhydric alcohol and omega-omegadicarboxylic alpihatic acid havingat least a six-carbon straight chain.The various forms of cable construction and variations in the protectingsleeve which are permitted by the invention are expressed in theappended claims.

Reference is made to applicants copending application Serial No. 73,797,filed April 10, 1936,

covering the coating composition per se.

We claim: I

l. A flexible insulated electrical conductor particularly useful asignition cable for internal combustion engines and capable of attaininga temperature of 325 1'. without loss of its effective properties,comprising a conductor, a rubber base insulating sleeve housing saidconductor, a cellulose covering over said rubber sleeve, and aprotective film over said covering, said film comprising the essentialcombination of cellulose ether as a base containing ethyl cellulose asan essential ingredient, as a modifying agent an ester of a polyhydricalcohol and an omegaomega dicarboxylic acid having at least a six carbonstraight chain, a lubricating agent, and a fire-proofing agent.

2. Flexible electric cord or cable which is particularly suitable towithstand use as ignition cable for internal combustion engines,comprising a flexible conductor, a flexible insulating sleeve ofrubber-base material over said conductor which is subject to injury ordestruction by oil or ozone, a flexible fabric cover over said sleeve ofmaterial normally subject to deterioration and destruction at elevatedtemperature, and a coating material over said fabric cover which coatingI material when on the cable is capable of attaining a' temperature of325 F. without loss of its effective protective properties or of theeffective properties of the cord or cable as a whole upon attaining saidtemperature or thereafter at lower temperatures, said coating materialcomprising cellulose ether of which ethyl cellulose is an essentialpart, and as a modifying agent an ester of a polyhydric alcohol and anomega-omega dicarboxylic aliphatic acid having at least a sixcarbonstraight chain.

3. Flexible electric cord or cable which is particularly suitable towithstand use as ignition cable for internal combustion engines,comprising a flexible conductor, an insulating sleeve of rubberbasematerial which is subject to injury or destruction by oil or ozone, anda coating material over said insulating sleeve which coating material onthe cord or cable is capable of attaining a temperature of 325 F.,without loss of its effective protective properties or of the effectiveproperties of the cord or cable as a whole upon attaining saidtemperature or thereafter at lower temperatures, said coating materialcomprising cellulose ether of which ethyl cellulose is an essentialpart, and as a modifying agent an ester of a polyhydric alcohol and anomega-omega dicarboxylic aliphatic acid having at least a six-carbonstraight chain.

4. Flexible electric cord or cable which is particularly suitable towithstand use as ignition cable for internal combustion engines,comprising a flexible conductor, a flexible insulating sleeve over saidconductor, a flexible fabric cover over said sleeve of material normallysubject to deterioration and destruction at elevated temperature, and acoating material over said fabric cover which coating material on thecord or cable is capable of attaining a temperature of 325 1",, withoutloss of its effective protective properties or of the effectiveproperties of the cord or cable as a whole upon attaining saidtemperature or thereafter at lower temperatures, said coating materialcomprising cellulose ether of which ethyl cellulose is an essentialpart, and as a modifying agent an ester of a polyhydric alcohol and anomega-omega dicarboxylic aliphatic acid having at least a six-carbonstraight chain.

5. In a flexible electric cord or cable which is particularly suitableto withstand use as ignition cable for internal combustion engines,having a flexible conductor, a flexible insulating sleeve and a flexiblefabric cover over said sleeve which is normally subject to deteriorationand destruction at elevated temperature, the combination with saidfabric cover of a coating material thereon which coating material on thecord or cable is capable of attaining a temperature of 325 F., withoutloss of its effective protective properties or of the effectiveproperties of the cord or cable as a whole upon attaining saidtemperature or thereafter at lower temperatures, said coating celluloseis an essential part, and as a modifying agent an ester of a polyhydrioalcohol and an omega-omega dicarboxylic aliphatic acid having at least asix-carbon straight chain.

6. In a flexible electric cord or cable whichis particularly suitable towithstand use as ignition cable for internal combustion engines, havinga flexible conductor and a flexible insulating sleeve, the combination"with said sleeve of u flexible fabric cover over said sleeve ofmateriai which is normally subject .to deterioration and destruc-v tionat elevated temperature, and a coating material on said cover, whichcoating material on the. cord or cable is capable of attaining atemperature of 325 F., without loss oi its effective protectiveproperties or of the effective properties of the cord or cable as awhole upon attaining said temperature or thereafter at lowertemperatures, said coating material comprising cellulose ether of whichethyl cellulose is an essential part,

and as a modifying agent an ester of a polyhydric alcohol and anomega-omega dicarboxylic aliphatic acid having at least a six-carbonstraight chain.

7. In a flexible electric cord or cable which is particularly suitableto withstand use as ignition cable. for internal combustion engines,having a flexible conductor and a flexible insulating sleeve, thecombination with said sleeve of a flexible fabric cover over said sleeveof material which is normally subject to deterioration and destructionat elevated temperature, and protective coating material on the materialof said fabric cover which coating material on the fabric on the cord orcable is capablcof attaining a temperature of 325 FL, without loss ofits effective protective properties or of the efl'ective properties ofthe cord or cable as a whole upon attaining said temperature orthereafter at lowertemperatures, said coating material comprisingcellulose ether of which ethyl cellulose is an essential part, and as amodifying agent an ester of a polyhydric alcohol and an omega-omegadicarboxylic aliphatic acid having at least six-carbon straight chain.

8. In a flexible electric cord or cable having a,

conductor, insulation on said conductor comprising a cellulosicmaterial, and a protective coating material therefor which coatingmaterial on the cord or cable is capable of attaining a temperature of325 F. without loss of its eiiective protective properties or of theefiectlve properties of the protected celluloslc material upon attainingsaid temperature orthereafter at lower ter'nperatures. said materialcomprising cellulose ether of which ethyl ccllulosc'is an essentialpart.- and as a modifying agent an ester of a polyhydric alcohol and anomega-omega dicarboxylicl aliphatic acid having at least a six-carbonstraight chain. A

9. Flexible electric cord "or-cable which is particularly suitable towithstand use as ignition cable for internal combustion engines,comprising a flexible conductor, an insulating sleeve of rubber-basematerial which is subject to injury or destruction by oil or ozone, anda. coating material over said insulating sleeve which coating materialon the cord or cable is capable of attaining a. temperature of 325 F.,without loss of its effective protective properties crof the effectiveproperties of the cord or cable as a whole upon attaining saidtemperature or thereafter at lower temperatures, said coating materialcomprising rial on the cord or cable is capable of attaining atemperature of 325 F., without loss of its eflective protectiveproperties or of the effective.-

properties of the cord or cable as a whole upon attaining saidtemperature or thereafter at lower temperatures, saidcoating materialcomprising cellulose ether of which ethyl cellulose is an essentialpart, and as a modifying agent an ester of glycerol and an omega-omega.dicarboxylic aliphatic-acid having at least a six-carbon straight chain.l

11. Flexible electric cord or cable which is particularly suitable towithstand use as ignition cable for internal combustion engines,-comprisingva flexible conductor, an insulating sleeve of' rubber-basematerial which is subject to injury by destruction by oil or ozone, anda coating material over said insulating sleeve which coating material onthe .cord or cable is capable of attalning a temperature of 325 F.,;without loss of its eifcctlve protective properties ;or oi the effectiveproperties of the cord or cable as a whole upon attaining saidtemperature or thereafter at lower temperatures, said coating materialcomprising cellulose cther of which ethyl cellulose is an essentialpart. and as s modifying agent an ester of glycol and sebacic acid.

12. Flexible electric cord or cable which is particulsrly suitable towithstand use as ignition cable for internal combustion engines,comprising a flexible conductor, an insulating sleeve of rubber-basematerial which is subect to injury or destruction by oil or ozone, and acoating matcrisl over said insulating sleeve which coating material onthe cord. or cable is capable of at.- taining a temperature of 825 1''.,without loss of its elective protective properties or ofthe effectivcproperties of the cord or cable as a whole.

prising cellulcsc other of which ethyl cellulose is Q an essential part.and as 's modifying agent on r ester of glycerol 'sndscbacic acid.

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